This invention relates an improved deflection yoke for a color cathode ray tube.
It has been proven by experiment that a deflection yoke for a color cathode ray tube with in-line or delta electron gun assemblies can be formed which generates a pincushion distribution vertical deflection magnetic field to correct the right and left side distortion of the raster. This deflection yoke also can be formed to generate a pincushion distribution horizontal deflection magnetic field to correct the upper and lower side distortion of the raster. Raster distortion is largely dependent on the magnetic field generated at the portion of the deflection yoke which corresponds to the cone portion of the cathode ray tube. It is also well understood that, in order to prevent three electron beams from causing convergence error, the sum of the vertical deflection magnetic field generated in the vicinity of the deflection yoke, which corresponds to the area between the neck and cone portions of the cathode ray tube, must be a barrel distribution. On the contrary, the sum of the horizontal deflection magnetic field must be a pincushion distribution.
The prior art deflection yoke of the so-called self-convergence type is formed to generate a barrel distribution in the vertical deflection field and a pincushion distribution in the horizontal deflection magnetic field. In such yoke, satisfactory convergence characteristics of electron beams and correction of upper and lower side pincushion distortion of the raster can be obtained. However, distortion of the right and left side pincushion of the raster is increased.
At the present time, in order to correct the right and left side pincushion distortion of the raster, a correcting circuit is used to produce an output signal in synchronism with a vertical signal. The output signal has an amplitude which varies in a parabolic form and the signal is superimposed on the horizontal deflection signal. However, such a correcting circuit adds components, increases cost and increases the complexity of the construction.